The present invention relates to a pump body for a medical gear pump for sucking and irrigating, with a pot-like pump housing with two cylindrical openings overlapping one to another, in which openings two meshing gearwheels are arranged, namely a driving gearwheel and a driven gearwheel. The driving gearwheel is, without a pivot bearing, arranged in the corresponding opening. Each opening is connected to an inlet and to an outlet. A lid is provided for closing the pot-like pump housing.
Such a pump body for a medical gear pump is known from DE 197 25 462 A1.
In the medical gear pump for sucking and irrigating described, both gearwheels meshing with each other via a spiral gearing, are embedded without pivot bearing in the openings of the pump body. The pot-like pump body is closed via a lid being trespassed by a coupling pin of the driving gearwheel. Each opening is in connection with an inlet connection piece and an outlet connection piece, which, in that way, form an inlet and an outlet of the medical gear pump.
The assembly of pump housing, lid and the meshing gearwheels embedded therein form a compact pump body, which is connectable with a drive body via a bayonet connection, in such a way that the coupling pin protruding from the driving gearwheel engages into a corresponding coupling slit of the drive body.
In order to clean the medical gear pump, the pump body is unlocked by the drive body via the bayonet connection, the lid is taken off, so that both gearwheels can be pulled out of the openings of the pump body.
After being cleaned and sterilized, both gearwheels can be pushed back, the lid can be applied and the pump body being assembled in such a way can be put on to the drive body again.
To avoid bacteria niches and to facilitate cleaning, this medical gear pump does not contain trunnion bearings for the two gearwheels in the openings.
When the gearwheels are taken off from the pump housing, the inner part of the pump housing contains merely the cylindrical openings, which can easily be cleaned and sterilized.
It was experienced in practical use that the driven gearwheel, i.e. the gearwheel which is not directly driven is pressed against the inner wall of the pump housing not only by the difference pressure between inlet and outlet, but also by the drive of the driving gearwheel during operation. When the flow resistance is high, this fact may result in high wear by abrasion, if the material the driven gearwheel is made of is not selected for optimal gliding conditions or if the fittings of the gearwheels to the housing bores are not precisely performed. Permanent operation, with a high load, results in a relatively strong generation of heat within the pump housing. Consequently, a relatively higher torque is required to create high feed pressures. This increased torque, however, requires stronger coupling pins and drive pins of the driving gearwheel. In order to prevent that, the coupling pin may be equipped with a relatively high diameter, which results, however, in a relatively high wear at the shaft seal as a consequence of an increased circumferential speed. The coupling pin protruding from the pump body has to pass the bottom of the pump body surrounded by a seal.
If the gear pump is intended to be used in multiple or permanent operation, the material of the housing and the gearwheels turning within needs to match in an optimum manner which requires hard materials with very good sliding properties.
This requires high quality materials and precisely manufactured components.
It is, therefore, an object of the present invention to manufacture a pump body, which shows good pump performances, but is cost-saving.
This object is achieved by a trunnion protruding from the bottom of the pump housing onto which trunnion the driven gearwheel is pushed onto.
The driven gearwheel is guided by the trunnion. The driven gearwheel, except within predetermined tolerances, is not extensively pressed against the inner wall of the pump housing by the driving gearwheel.
Thus, it is not necessary to use particularly wear-resistant materials, which were precisely manufactured. The materials used are cost-saving materials. The same applies for the material of the pump housing.
Pressure force peaks acting from the wall of the housing openings onto the curved lines of the soft elastic tooth tips of the driven gearwheel are taken up by the trunnion. The tooth tips of the driven gearwheel are more charged than the respective tips of the driving gearwheel. The pressure force peaks taken up by the trunnion are forces in the range of the elastic deformability of the material the teeth are made.
Material abrasion at the driven gearwheel is thus prevented. A possible wobbling of the gearwheels within the clearance of the overlapping openings is strongly reduced.
This design is useful to make a single use pump body. The requirements of the materials are merely that one single use is safely ensured. This offers the possibility to use cheap injection molding materials with relatively large clearances to produce pump housings as well as gearwheels.
A simple handling and a simple mounting of the pump is possible, as the trunnion serves as orientation feature and centering aid for the driven gearwheel while mounting.
After using of the pump, the pump body can be turned off the drive body via the bayonet connection and can be disposed, and for the next use of the pump a new pump body can be mounted.
In a preferred embodiment of the invention, the trunnion is molded to the bottom of the pump housing.
This measurement has the advantage that the bearing trunnion is simultaneously molded or injected to the bottom of the pump housing when the pump housing is manufactured so that it is possible to manufacture the pump housing in a particular simple and cost-saving way.
In a further embodiment of the invention, the trunnion is slightly conical.
This measurement has the advantage in view of manufacturing that a conical trunnion can be much more easily removed from an injection tool than a cylindrical trunnion. Due to the conical shape it is also easy to center the gearwheel while mounting and in operation.
Both the driving gearwheel and the driven gearwheel can be manufactured as simple injection molded parts which are mounted into the pump housing, which is also designed as a injection molded part, and the pump housing then closed via the lid. All of these parts can be manufactured with less technical effort and cheaply. Therefore, a pump body is available for one single use, which, nevertheless, allows relatively strong drive forces with a safe and sufficient pump performance.
It is understood that the afore-mentioned features and the features to be explained later cannot only be used in the combinations mentioned, but can also be used in other combinations or solely without leaving the scope of the present invention.